Air circulation inside the buses' cabin seems to negatively affect the spread of contagious diseases, such as the COVID-19 virus and raises valid health concerns over using public transportations. Employing all-fresh air and avoiding to recirculate it could help with lowering the exposure time and the virus density in buses; however, it makes the heating more challenging, especially in Electric buses. Here a Baseline and a proposed Recovery Heat Pump (BHP and RHP, respectively) systems in a generic single decker bus were modeled to investigate their dynamic performance and the cabin's conditions using 100% fresh air. Simulink and Simscape toolbox from MATLAB (R2020a) were used to build up the real-time model by integrating an HP system with a cabin sub-model. The cabin is modeled using a moisture air network and is coupled with the HP to exchange heat with the refrigerant through the condenser. For both cases, 100% fresh air flows through the condenser into the cabin. In BHP the evaporator is exposed to 100% cold fresh air, while in RHP the warm air from the cabin passes through the evaporator before being vented outside. Both cases were studied for different ventilation modes in low and medium occupancy levels. Results indicate that RHP shows superior performance compared with BHP. Under the studied operational conditions, RHP reduced the power requirement, warm-up time, and operation time by 36%-6% (at most-at least), 57%-7%, and 39%-13%, respectively.
In the present paper, the Eulerian-granular model is adopted, to predict the frost growth on one channel of a plate-fin evaporator. A proper mass transfer model and modified frosting criteria are used to simulate the frost formation process. First, the model is validated with experimental data obtained under various operating conditions. The numerical predictions for the frost thickness and density are in good agreement with available experimental data. Furthermore, a parametric analysis is carried out to study the impact of the geometrical parameters of a three-dimensional plate-fin evaporator. A qualitative comparison shows a good agreement between the numerical data and experimental observations reported in the literature. One interesting outcome emerging from this study is that the distance between refrigerant tubes can play an important role in the frosting time.
In this paper, the performance of a compact Three-Fluid Combined Membrane Contactor (3F-CMC) is investigated using Computational Fluid Dynamics (CFD), supported and validated with a good agreement by an experimental campaign made on a fully working prototype. This internally-cooled membrane contactor is the core component of a hybrid air conditioning system for electric vehicles (EVs) developed in a successful H2020 project called XERIC. In the adopted numerical approach, the conjugate heat and mass transfer inside the 3F-CMC is described by non-isothermal incompressible flows and vapor transport through a PTFE hydrophobic membrane. The sensitivity of the 3F-CMC performance to air/desiccant flow rates, temperature, humidity, and desiccant concentration is analyzed numerically through the validated CFD codes. According to this study, the moisture removal increases by the inlet humidity ratio, nearly linearly. Under the considered conditions (where the inlet air temperature is 26.2 °C), when the inlet relative humidity (RH) is 75% the moisture removal is about 450% higher than the case RH = 37%, while the absorption effectiveness declines about 45%. Furthermore, this study shows that the amount of absorbed vapor flux rises by increasing the airflow rate; on the other hand, the higher the airflow rate, the lower is the overall absorption efficiency of the 3F-CMC. This investigation gives important suggestions on how to properly operate a 3F-CMC in order to achieve the requested performance, especially in hot and humid climates.
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